1. Field of the Invention
The present invention relates to digital frequency discrimination.
2. State of the Art
Frequency discrimination is important in digital radio communications, in particular in any digital FM radio receiver. Frequency discrimination is typically performed using analog circuitry, e.g. an IQ frequency discriminator. Analog frequency discriminators have substantial drawbacks. In the case of an IQ frequency discriminator, the discriminator requires a number of analog components, two A/D conversions and a numerical arctangent operation, rendering the circuit quite complex.
Known methods exist for producing a value representing the instantaneous frequency of a signal using only digital logic elements. Various such methods are described in U.S. Pat. No. 5,084,669, incorporated herein by reference. In particular, the foregoing patent describes a digital circuit for determining the instantaneous phase of a signal, from which the instantaneous frequency may be obtained if desired. Although the implementation of the circuit is all digital, it is quite involved. An improved method and apparatus for determining in a simple, all-digital manner the instantaneous frequency of a signal would therefore likely be well-received by those skilled in the art.